Answer:
ALEX AND HER SISTER TAKE TURNS IN WATERING THEIR FLOWER IN THE GARDEN.
HER TURNS TO WATER THEIR ROSES IS EVERY 4 DAYS AND THEIR ORCHIDS EVERY 8 DAYS. SUPPOSED ALEX WATERED BOTH ROSES AND ORCHIDS ON THE 3RD DAY OF THE MONTH, WHEN WILL ALEX TURN TO WATER THEM AGAIN?
i just got it somewhere, and i hope it helps<3